This invention relates to a zoom lens barrel which is provided with an optical system including a first lens group which is moved for focusing and also for zooming by a single operating ring.
Published Unexamined Japanese Utility Model Application No. Sho 53-82341 discloses a zoom lens barrel of the foregoing type. With the disclosed lens barrel, the lens system and barrel head ring are rotated with the rotation of an operating ring, so that the barrel has the drawback that when the lens system is misaligned even if only slightly, a group of lenses will be shifted to an eccentric position, for example, during zooming. Such a lens barrel has another drawback in that when a polarizing filter or square hood is attached to the barrel head ring, the direction of polarization is likely to change or an eclipse is liable to take place.
Further, since the operating ring also axially shifts during focusing, it is impossible to maintain the axial position of the operating ring per se in corresponding relation to the focal distance. This gives rise to the necessity of providing an additional member such as a focusing scale ring.
It is thus an object of the present invention to eliminate the eccentricity of a first group of movable lenses relative to a second group of movable lenses that would arise during zooming.
Another object of the present invention is to overcome the above-mentioned drawback which occurs when the first group of movable lenses is shifted with an attachment mounted on the barrel head ring.
Still another object of the present invention is to provide a zoom lens barrel of simplified construction which has a single operating ring and in which there is no need to provide an additional member, such as a focusing scale ring, for the indication of both the focal distance and the photographic distance.